How are you suppose to stimulate your nipples to induce labor??

I've rubbed my palm over them for over an hour and all out hand expressed milk for an hour and the next day for a half hour. I haven't gotten a single contraction. Am I just doing it wrong? Is there an effective way to do it? Do you need lotion or a type of lubricant? I'm just confused. I've never heard of it not even inducing contractions at all. I've always heard them coming and leaving but I can't even get one.